Current measuring device

ABSTRACT

A current measuring device in which the current flow produced by a corona generating device is detected. The device measures the spatial distribution of the current flow from the corona generating device.

United States Patent [191 Hayne et a1.

[451 Nov. 26, 1974 CURRENT MEASURING DEVICE [75] Inventors: Thomas F.Hayne, Fairport; Ross E.

Schroll, Rochester, both of NY.

[73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: June 21, 1973 [2]] Appl. No.: 372,436

[52] US. Cl. 317/262 A, 324/32, 324/725 [51] Int. Cl. H01t 19/00 [58]Field of Search 317/262 A; 324/32, 33, 324/72, 72.5

[5 6] References Cited UNITED STATES PATENTS 3,358,378 12/1967 Downs324/32 3,739,246 6/1973 Haas 317/262 A Primary Examiner-J. D. MillerAssistant E.raminerHarry E. Moose, Jr.

Attorney, Agent, or FirmH. Fleischer; J. J. Ralabate; C. A. Green [57]ABSTRACT A current measuring device in which the current flow producedby a corona generating device is detected. The device measures thespatial distribution of the current flow from the corona generatingdevice.

18 Claims, 4 Drawing Figures CURRENT MEASURING DEVICE BACKGROUND OF THEINVENTION This invention relates generally to a multi-colorelectrophotographic printing machine, and more particularly concerns acurrent measuring device adapted to detect the spatial distribution ofthe current flow from a corona generating device utilized in theelectrophotographic printing machine.

In a typical electrophotographic printing machine, a photoconductivesurface is electrostatically charged to a substantially uniformpotential over the entire surface thereof, and then exposed to a lightimage of the original document being reproduced. The light imageselectively discharges the photoconductive surface in the irradiatedareas to form an electrostatic latent image thereof. The electrostaticlatent image is then developed by contacting it with finely dividedelectrostatically attractable material, such as toner particles.Thereafter, the developed image is transferred to a suitable sheet ofsupport material, such as paper, amongst others. The powder imagetransferred to the support material is subsequently suitably affixedthereon to form a permanent copy of the original document.

In multi-color electrophotographic printing successive electrostaticlatent images are formed on the photoconductive surface, each imagerepresenting a particular color in the original. In this type ofprinting, a plurality of single color toner powder images aretransferred to the sheet of support material in superimposedregistration with one another. Hence, multi-color electrophotographicprinting requires a plurality of tonerpowder images whereas black andwhite or single color printing requires only a single toner powderimage. It is, therefore, evident that the amount of toner particles usedin the formation of a multi-color copy is significantly greater thanthat required for the production of a single color copy. The increasedamount of toner powder used in a multi-color electrophotographicprinting machine substantially increases the contamination from dust andtoner particles. In any electrophotographic printing machine there is aneed to make sim ple and repeatable measurements of the effect of dirton the corona generating device. This is particularly true in the caseof a multi-color electrophotographic printing machine wherein largeamounts of dust or toner particles are formed due to the large amount oftoner powder utilized therein.

The corona generating device develops a spray of ions which is depositedon the photoconductive surface to provide a substantially uniform chargethereon. However, as dirt or toner particles are deposited on thecoronode wires or grid wires of the corona generating device, thecurrent flow from the corona generating device to the photoconductivesurface varies as a function of the contamination thereon. Hence, theuniformity of the charge deposited on the photoconductive surface willvary along the length of the coronode wire depending upon the extent ofthe contamination thereon.

Accordingly, it is the primary object of the present invention toimprove detection of the spatial distribution of the current flow from acorona generating device utilized in an electrophotographic printingmachine.

SUMMARY OF THE INVENTION Briefly stated, and in accordance with thepresent invention, there is provided a device for measuring the spatialdistribution of the current flow from a corona generating device.

In the present instance, the device includes corona generating means,accumulating means and current sensing means. The corona generatingmeans forms a spray of ions which are deposited on the accumulatingmeans. Pursuant to the present invention, the accumulating means has aplurality of substantially equally spaced electrically conductiveportions insulated from one another. The sensing means is in electricalcommunication with the accumulating means. In this manner, the sensingmeans measures the current flow at each electrically conductive portionof the accumulating means. This determines the spatial distribution ofthe current flow from the corona generating device in the longitudinaldirection thereof.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of thepresent invention will become apparent upon reading the followingdetailed description and upon reference to the drawings, in which:

FIG. 1 is a schematic perspective view of a multicolorelectrophotographic printing machine incorporating a corona generatorwhich requires the spatial distribution of the current flow therefrom tobe measured;

FIG. 2 is a schematic perspective view of the FIG. 1 corona generatorassociated with the current measuring device of the present invention;

FIG. 3 is an elevational view of the FIG. 2 current measuring device;and

FIG. 4 is a schematic electrical diagram of the FIG. 2 current measuringdevice.

While the present invention will be described in connection with apreferred embodiment, it will be understood that it is not intended tolimit the invention to that embodiment. On the contrary, it is intendedto cover all alternatives, modifications and equivalents as may beincluded within the spirit and scope of the invention as defined by theappended claims.

DETAILED DESCRIPTION OF THE INVENTION For a general understanding of thedisclosed multicolor electrophotographic printing machine having acorona generator incorporated therein for utilization in conjunctionwith the current measuring device of the present invention, continuedreference is had to the drawings. In the drawings, like referencenumerals have been used throughout to designate like elements. Turningnow to FIG. l,'the various components of the multicolor printing machineare depicted schematically therein. Although the current measuringdevice of the present invention will be described in conjunction withthe corona generator of the FIG. 1 printing machine, it is particularlywell adapted for use with any type of corona generator. Hence, it willbecome evident from the following discussion that the current measuringdevice is well suited for use with a wide variety of corona generators,and is not necessarily limited to the particular embodiment shownherein. Initially, the multi-color electrophotographic printing machinewill be described in its normal process mode. Thereafter, the printingmachine will be described with the photoconductive drum removedtherefrom and the current measuring device of the present inventionincorporated therein in association with the corona generator thereof soas to determine the spatial distribution of the current flow therefrom.

The normal process mode of the multi-color electrophotographic printingmachine disclosed in FIG. 1 will now be described. Theelectrophotographic printing machine utilizes a drum having aphotoconductive surface 12 secured to and entrained about the exteriorcircumferential surface thereof. Drum 10 is mounted rotatably on themachine frame and driven at a substantially constant angular velocity,in the direction of arrow 14, by a drive motor (not shown). As drum 10rotates, photoconductive surface 12 advances sequentially through aseries of processing stations. The drive motor rotates drum 10 at apredetermined speed relative to the other operating mechanisms of theprinting machine. A timing disc mounted in the region of one end of theshaft of drum 10 cooperates with the machine logic to synchronize thevarious machine operations with the rotation of drum 10. In this manner,the proper sequence of events is produced at the respective processingstations.

Initially, drum 10 rotates photoconductive surface 12 through chargingstation A. At charging station A, a suitable corona generator, indicatedgenerally at 16, extends longitudinally in a transverse direction acrossphotoconductive surface 12. Corona generator 16 is designed to sprayions onto photoconductive surface 12 to produce a relatively high,substantially uniform charge thereon. The charge distribution or thecurrent profile produced by corona generator 16 is, preferably,subustantially uniform in the longitudinal direction to generate asubstantial uniform charge on the photoconductive surface in thelongitudinal direction. However, frequently the accumulation of dirt ortoner particles on corona generator 16 will degradate the current flowtherefrom producing deviations in charge across photoconductive surface12. The foregoing charge deviations may also result if the coronagenerator is not aligned such that it is substantially parallel to andspaced from the photoconductive surface 12. Occasionally coronagenerator 16 is skewed relative to photoconductive surface 12 resultingin a non-uniform charge across photoconductive surface 12. The currentmeasuring device of the present invention is adapted to determine thecurrent flow distribution in the longitudinal direction of coronagenerator 16. Corona generator 16 will be described hereinafter indetail with reference to FIG. 2.

- After photoconductive surface 12 is charged to a substantially uniformpotential, drum 10 rotates to exposure station B. At exposure station B,a color filtered light image of original document 18 is projected ontocharged photoconductive surface 12. Exposure station B includes a movinglens system, generally designated by the reference numeral 20, and acolor filter mechanism shown generally at 22. A suitable moving lens.system is disclosed in U.S. Pat. No. 3,062,108 issued to Mayo in 1962.Original document 18, such as a sheet of paper, book, or the like isdisposed face down upon transparent viewing platen 24. As shown in FIG.1, lamps 26 are adapted to move in a timed relationship with lens 20 andfilter mechanism 22 to scan successive incremental areas off originaldocument 18 disposed upon platen 24. This produces a flowing light imageof original document 18 which is projected onto charged photoconductivesurface 12. Filter mechanism 22 is arranged to interpose selected colorfilters into the optical light path of lens 20. The filter operates onthe light rays transmitted throughlens 20 to record an electrostaticlatent image on photoconductive surface 12 corresponding to apreselected spectral region of the electromagnetic wave spectrum,hereinafter referred to as a single color electrostatic latent image.

After the electrostatic latent image is recorded on photoconductivesurface 12, drum 10 rotates to development station C. At developmentstation C, three individual developer units, generally indicated by thereference numerals 28, 30 and 32, respectively, render visible theelectrostatic latent image recorded on photoconductive surface 12.Preferably, the developer units are all of a type generally referred toas magnetic brush developer units. Each of the developer units containappropriately color toner particles corresponding to the complement ofthe spectral region of the wave length of light transmitted throughfilter 20. By way of example, a green filtered electrostatic latentimage is developed by depositing green absorbing magenta toner particlesthereon. Similarly, blue and red filtered latent images are developedwith yellow and cyan toner particles, respectively.

After development, the now visible toner powder image is advanced totransfer station D. At transfer station D, the toner powder imageadhering electrostatically to photoconductive surface 12 is transferredto a sheet of final support material 34, Final support material 34 maybe, plain paper or a sheet of thennoplastic polysulfone maten'al,amongst others. A transfer roll, shown generally at 36, secures supportmaterial 34 releasably thereon for movement in a recirculating paththerewith. Transfer roll 36 is adapted to rotate in synchronism withdrum 10, in the direction of arrow 38, at substantially the same angularvelocity therewith. This readily enables a plurality of toner powderimages to be transferred from photoconductive surface 12 to supportmaterial 34 in superimposed registration with one another. U.S. Pat. No.3,612,677 issued to Langdon et al. in 1971 describes a transfer rollelectrically biased to a sufficient magnitude and the proper polarity toattract toner particles from photoconductive surface 12 to supportmaterial 34.

Prior to proceeding with the description of fusing apparatus 58 disposedat fixing station E, the sheet feeding path will be briefly discussed. Astack 40 of sheet material 34 is disposed on tray 42. Feed roll 44cooperating with retard roll 46 separates and advances successiveuppermost sheets from stack 40. The advancing sheet moves into chute 48which guides it into the nip of register rolls 50. Register rolls 50forward the advancing sheet to transfer roll 36 where gripper fingers 52secure the sheet thereon. After a plurality of toner powder images havebeen transferred to support material 34 gripper fingers 52 space supportmaterial 34 from transfer roll 36 permitting stripper bar 54 to beinterposed therebetween. In this manner, support material 34 is strippedfrom transfer roll 36 and advanced on endless conveyor 56 to fixingstation E.

At fixing station E, fuser 58 permanently affixes the multi-layeredtoner powder image to support material 34. The toner powder image isgenerally heat settable and one type of suitable fuser arranged to fixthe toner powder image is described in US. Pat. No. 3,493,592 issued toMoser et al. in 1970. After the toner powder image is fused to supportmaterial 34, support material 34 is advanced by endless conveyors 60 and62 to catch tray 64. Catch tray 64 is suitably arranged to permit themachine operator to readily remove the completed multi-color copy fromthe printing machine.

The last processing station in the direction of rotation of drum 10, asindicated by arrow 14, is cleaning station F. As previously indicated, apreponderance of the toner particles are transferred to support material34, however, some residual toner particles remain on photoconductivesurface 12. Cleaning station F removes these residual toner particlesfrom photoconductive surface 12. The residual toner particles areinitially brought under the influence of a corona generating device (notshown) adapted to neutralize the remaining electrostatic charge onphotoconductive surface 12 and the residual toner particles. Thereafter,the neutralized toner particles are cleaned from photoconductive surface12 by rotating fibrous brush 66. One type of suitable brush cleaningdevice is described in US.

- Pat. No. 3,590,412 issued to Gerbasi in 1971. It should be noted thatin addition to removing the toner particles, cleaning station F levelsthe charge remaining on photoconductive surface 12 so that coronagenerator 16 may recharge photoconductive surface 12 to the requisitedesired potential. In this manner, photoconductive surface 12 may berepeatedly charged to substantially the same level for each successivesingle color electrostatic latent image. Hence, it is of paramountimportance to have corona generator 16 adapted to charge photoconductivesurface 12 to a substantially uniform level. Any degradation in chargeproduced by corona generator 16 must be identified. As heretoforeindicated, degradations in charge may be used by an accumulation of dirton corona generator 16 or the skewness thereof relative tophotoconductive surface It is believed that the foregoing description issufficient to illustrate the general operation of a multi-colorelectrophotographic printing machine. Moreover, the foregoing discussionhas indicated a need for determining the spatial distribution of thecurrent flow developed by corona 16 so as to evaluate the uniformity ofthe charge deposited on photoconductive surface 12. FIGS. 2 through 4,inclusive, will be discussed hereinafter to provide a detaileddescription of the current measuring device utilized in conjunction withcorona generator 16 to insure that the charge or current flow producedtherebyis substantially uniform in a longitudinal direction.

Referring now to FIG. 2, drum is removed from the FIG. 1 printingmachine and current measuring device 68 placed therein in lieu thereof.Coronagenerator 16 is described in detail in FIG. 2. As depictedtherein, corona generator 16 includes an elongated shield 70 preferablymade from a conductive material such as an aluminum extrusion. Elongatedshield 70 is substantially U-shaped'and may be grounded or, in lieuthereof, biased to a suitable electrical voltage level. A pairofdischarge electrodes 72 and 76 are mounted in the chamber defined byU-shaped shield 70. Discharge electrodes 72 and 76 are, preferably,coronode wires approximately 0.0035 inches in diameter and extendlongitudinally along the length of shield 72. Coronode wires 72 and 76are made preferably from a suitable platinum material. Coronode wires 72and 76 are suitably excited to produce a flow of ions therefrom. The ionflow is adapted to be deposited on current measuring device 68 so thatthe current flow along the longitudinal axis of coronode wires 72 and 76may be evaluated. Grid means or a plurality of substantially parallel,spaced, fine conductive wires 74 extend in a longitudinal direction fromone end of shield to the other end thereof and across about threefourths of the open end of the chamber therein. Coronode wires 72 and 76are secured to an insulating plate (not shown) mounted on the ends ofshield 70. As depicted in FIG. 2, coronode wire 72 is positioned in theportion of the chamber of shield 70 that is covered vby grid wires 74.Coronode wire 76 is disposed in the open portion of the chamber ofshield 70, Le, the portion not covered by grid wires 74. As heretoforeindicated, current measuring device 68 replaces photoconductive drum 10in the electrophotographic printing machine of FIG. 1. Current measuringdevice 68 is located such that the surface thereof is spacedsubstantially the same distance from corona generator l6asphotoconductive surface 12. Current measuring device 68 includes currentsensing means 78 and accumulating means 80. Accumulating means 80includes a plurality of substantially equally spaced electricallyconductive portions 82 insulated from one another. Electricallyconductive portions 82 are mounted on an elongated surface 84. Elongatedsurface 84 is illustrated in detail in FIG. 3. In the preferredembodiment of the present invention twenty three electrically conductiveportions 82 are mounted on elongated surface 84. Preferably, elongatedsurface 84 may be formed from a printed circuit wiring board with 22guage wire electrically connected to each electrically conductiveportion 82 and to current sensing means 78. Current sensing means 78includes switch and ammeter 92. A sheet of insulating material 86,preferably made from 0.005 inches thick polyester, e.g., Mylar,extending about l0 inches in length and 2 inches in width is interposedbetween elongated surface 84 and arcuate member 88. Arcuate member 88 ispreferably made from a substantially rigid, conductive material such asaluminum. The curvature of arcuate member 88 duplicates that ofphotoconductive drum 10. In this manner, accumulating means 80 simulatesphotoconductive surface 12. Switch 90 is electrically connected to the23 conductive portions 82 of accumulating means 80. A suitable 24 pointswitch is Model No. 53 MY 21070 made by Grayhill, Inc. of Le Grange,Ill. Switch 90 in turn, is connected to a suitable ammeter 92. Byrotating knob 91, switch 90 connects successive electrically conductiveportions 82 to ammeter 92 to register the current flow from each of theelectrically conductive portions 82 independently determining thecurrent distribution in the longitudinal direction of coronode wires 72and 76, respectively. In this manner, the charge distribution onphotoconductive surface 12 may be evaluated and the uniformity thereofdefined. This permits the ready determination of whether or not coronagenerator 16 must be readjusted or cleaned.

Referring now to FIG. 3, there is shown a printed circuit representationof elongated surface 84. As shown therein 23 electrically conductiveportions 82 are spaced from one another by insulating means 94. Printedcircuit board 84 may be fabricated by suitable means such as by havingboth sides of an insulating board, e.g., glass reinforced epoxy, coatedwith a thin metal sheet, e.g., a thin sheet of copper. A chemicaletching process removes the copper in all areas except conductiveportions 82. In order to connect the electrical lead wires, i.e., 22guage wire, to board 84, each conductive portion 82 extends to a row ofuniformly spaced edge contacts 81 arranged to connect with the 22 gaugeexternal lead wires.

Turning now to FIG. 4, the operation of the present invention will bebriefly described. A portion of accumulating means 80 is depicted inFIG. 4 and includes a plurality of electrically conductive portions 82spaced from one another and electrically insulated from one another. Inaddition, accumulating means 80 includes a polyester sheet of insulatingmaterial 86 entrained about conductive arcuate number 88. In FIG. 4, onelead from switch 90 is electrically connected to ammeter 92. The otherlead is electrically grounded. In this way, only theelectrically'conductive portion 82 connected to the lead incommunication with ammeter 92 will record a reading thereon. Theremaining electrical portions 82 will be grounded and not produce areading on ammeter 92. Hence, by rotating knob 91 (FIG. 2) eachelectrically conductive portion 82 may have the current flow thereonread by ammeter 92 so as to determine the current flow distributionproduced thereon by corona generator 16.

An alternate electrical arrangement may be employed to measure thecurrent uniformity of a biased or simulated charged surface. In thistype of arrangement, a first resistor is connected in series withammeter 92 and electrically conductive portion 82 being meausred. Theremaining electrically conductive portions 82 are connected to anelectrical common, which, in turn, is connected to an electrical groundthrough a second series resistor. The voltage across the econd seriesresistor acts as a biasing potential. Similarly, the voltage across thefirst resistor is known by measuring the current passing therethrough,i.e., the current measured by LII modifications, andvariations as fallwithin the spirit and broad scope of the appended claims.

What is claimed is: 1. A current measuring device, including: coronagenerating means arranged to form a spray of ions; means, closely spacedto said corona generating means, for accumulating the ions formed bysaid corona generating means to produce a current flow, saidaccumulating means comprising a plurality of substantially equallyspaced electrically conductive portions insulated from one another; andmeans, in electrical communication with said accumulating means, forsensing the current flow on each portion of said accumulating means todetect the spatial distribution of the current flow produced by saidcorona generating means. 2. A device as recited in claim 1, wherein saidcurrent sensing means includes:

switch means in electrical communication with said accumulating means;and current measuring means in electrical communication with said switchmeans, said switch means being adapted to electrically connect eachportion of said accumulating means to said current measuring means todetect the current flow thereon. 3. A device as recited in claim 2,further including a pair of resistance elements, one of said resistancecleammeter 92. This enables the current uniformity of the biased surfaceto be evaluated. By way of example, the first resistor, in series withammeter 92, is preferably about 60 meg ohms, while the second resistor,in series with the grounded electrically conductive portions 82, isabout 600 meg ohms.

In recapitulation, the current measuring device of the present inventiondetermines the spatial distribution of the current flow produced by acorona generator. This enables the performance of the corona generatorto be evaluated. In multi-color electrophotographic printing, the coronagenerator must produce a substantially uniform current flow on thephotoconductive surface to develop a substantially uniform chargethereon. The foregoing is hindered by the accumulation of dust or theskewness of the corona generator relative to the photoconductivesurface. The utilization of the current measuring device of the presentinvention simulates the photoconductive surface to determine the currentflow distribution thereon.

Thus, it is apparent there has been provided, in accordance with thepresent invention, a current measuring device that fully satisfies theobjects, aims and advantages set forth above. While this invention hasbeen described in connection with specific embodiments thereof, it isevident that many alternatives, modifications, and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, it is intended to embrace all suchalternatives,

ments being electrically connected in series between said currentmeasuring means and the portion of said accumulating means in electricalcommunication therewith, the other of said resistance elements beingelectrically connected in series between the other portions of saidaccumulating means and an electrical ground.

4. A device as recited in claim 2, wherein said corona generating meansincludes:

an elongated shield defining an open ended chamber;

and

a corona discharge electrode disposed in the open ended chamber of saidshield.

5. A device as recited in claim 4, wherein said discharge electrodeincludes at least a pair of spaced substantially parallel conductivecoronode wires, said pair of coronode wires extending substantially in alongitudinal direction along the length of said shield.

6. A device as recited in claim 5, further including grid meanscomprising a plurality of spaced substantially parallel grid wiresmounted in said shield and extending substantially in a longitudinaldirection along the length thereof, said plurality of grid wirespartially enclosing the open end of said shield with one of the coronodewires being disposed in the chamber thcrebeneath, the other of saidcoronode wires being disposed in the unenclosed portion of the chamberof said shield.

7. A device as recited in claim 6, wherein said accumulating meansincludes an elongated surface having the electrically conductiveportions thereof arranged along discrete regions of the longitudinalaxis thereof, said elongated surface being closely spaced to said pairof coronode wires with the longitudinal axis of said elongated surfacebeing closely spaced from and substantially parallel to the longitudinalaxes of said pair of coronode wires, said elongated surface beingarranged such that each electrically conductive portion detects thecurrent flow from the discrete region opposed therefrom along thelongitudinal axes of said coronode wires.

8. A device as recited in claim 7, wherein said accumulating meansincludes:

a conductive arcuate member; and

an insulating sheet mounted on the exterior peripheral surface of saidarcuate member, said elongated surface being mounted on said insulatingsheet such that each electrically conductive portion extends from onemarginal region of said arcuate member to the other marginal regionthereof with each electrically conductive portion being located on adiscrete region of said arcuate member in the longitudinal directionthereof.

9. A device as recited in claim 8, wherein said elongated surfaceincludes a printed circuit board.

10. A device simulating a photoconductive surface forsensing the currentdistribution thereon in an electrophotographic printing machine of thetype having corona generating means spraying ions to create a charge onthe photoconductive surface, including:

means, closely spaced to the corona generating means, for accumulatingthe ions formed by the corona generating means to produce a currentflow, said accumulating means comprising a plurality of substantiallyequally spaced electrically conductive portions insulated from oneanother; and

means, in electrical communication with said accumulating means, forsensing the current flow on each portion of said accumulating means todetect the spatial distribution of the current flow produced by thecorona generating means.

11. A device as recited in claim 9, wherein said current sensing meansincludes:

switch means in electrical communication with said accumulating means;and

current measuring means in electrical communication with said switchmeans, said switch means being adapted to electrically connect eachportion of said accumulating means to said current measuring means todetect the current flow thereon.

12. A device as recited in claim 11, further including a pair ofresistance elements, one of said resistance elements being electricallyconnected in series between said current measuring means and the portionof said accumulating means in electrical communication therewith, theother of said resistance elements being electrically connected in seriesbetween the other portions of said accumulating means and an electricalground.

13. A device as recited in claim 11, wherein the corona generating meansof the electrophotographic printing machine includes:

an elongated shield defining an open ended chamber;

and

a corona discharge electrode disposed in the open ended chamber of saidshield.

14. A device as recited in claim 13, wherein said discharge electrodeincludes at least a pair of spaced substantially parallel conductivecoronode wires, said pair of coronode wires extending substantially in alongitudinal direction along the length of said shield.

15. A device as recited in claim 14, further including grid meanscomprising a plurality of spaced substantially parallel grid wiresmounted in said shield and extending substantially in a longitudinaldirection along the length thereof, said plurality of grid wirespartially enclosing the open end of said shield with one of the coronodewires being disposed in the chamber therebeneath, the other of saidcoronode wires being disposed in the unenclosed portion of the chamberofsaid shield.

16. A device as recited in claim 15, wherein said accumulating meansincludes an elongated surface having the electrically conductiveportions thereof arranged along discrete regions of the longitudinalaxis thereof. said elongated surface being closely spaced to said pairof coronode wires with the longitudinal axis of said elongated surfaceclosely spaced from and substantially parallel to the longitudinal axesof said pair of coronode wires, said elongated surface being arrangedsuch that each electrically conductive portion detects the current flowfrom the discrete region opposed therefrom along the longitudinal axesof said coronode wires.

17. A device as recited in claim 16, wherein said accumulating meansincludes:

a conductive arcuate member; and

an insulating sheet mounted on the exterior peripheral surface of saidarcuate member, said elongated surface being mounted on said insulatingsheet such that each electrically conductive portion extends from onemarginal region of said arcuate member to the other marginal regionthereof with each electrically conductive portion being located on adiscrete region of said arcuate member in the longitudinal directionthereof.

18. A device as recited in claim 16, wherein said elongated surfaceincludes a printed circuit board.

1. A current measuring device, including: corona generating means arranged to form a spray of ions; means, closely spaced to said corona generating means, for accumulating the ions formed by said corona generating means to produce a current flow, said accumulating means comprising a plurality of substantially equally spaced electrically conductive portions insulated from one another; and means, in electrical communication with said accumulating means, for sensing the current flow on each portion of said accumulating means to detect the spatial distribution of the current flow produced by said corona generating means.
 2. A device as recited in claim 1, wherein said current sensing means includes: switch means in electrical communication with said accumulating means; and current measuring means in electrical communication with said switch means, said switch means being adapted to electrically connect each portion of said accumulating means to said current measuring means to detect the current flow thereon.
 3. A device as recited in claim 2, further including a pair of resistance elements, one of said resistance elements being electrically connected in series between said current measuring means and the portion of said accumulating means in electrical communication therewith, the other of said resistance elements being electrically connected in series between the other portions of said accumulating means and an electrical ground.
 4. A device as recited in claim 2, wherein said corona generating means includes: an elongated shield defining an open ended chamber; and a corona discharge electrode disposed in the open ended chamber of said shield.
 5. A device as recited in claim 4, wherein said discharge electrode includes at least a pair of spaced substantially parallel conductive coronode wires, said pair of coronode wires extending substantially in a longitudinal direction along the length of said shield.
 6. A device as recited in claim 5, further including grid means comprising a plurality of spaced substantially parallel grid wires mounted in said shield and extending substantially in a longitudinal direction along the length thereof, said plurality of grid wires partially enclosing the open end of said shield with one of the coronode wires being disposed in the chamber therebeneath, the other of said coronode wires being disposed in the unenclosed portion of the chamber of said shield.
 7. A device as recited in claim 6, wherein said accumulating means includes an elongated surface having the electrically conductive portions thereof arranged along discrete regions of the longitudinal axis thereof, said elongated surface being closely spaced to said pair of coronode wires with the longitudinal axis of said elongated surface being closely spaced from and substantially parallel to the longitudinal axes of said paiR of coronode wires, said elongated surface being arranged such that each electrically conductive portion detects the current flow from the discrete region opposed therefrom along the longitudinal axes of said coronode wires.
 8. A device as recited in claim 7, wherein said accumulating means includes: a conductive arcuate member; and an insulating sheet mounted on the exterior peripheral surface of said arcuate member, said elongated surface being mounted on said insulating sheet such that each electrically conductive portion extends from one marginal region of said arcuate member to the other marginal region thereof with each electrically conductive portion being located on a discrete region of said arcuate member in the longitudinal direction thereof.
 9. A device as recited in claim 8, wherein said elongated surface includes a printed circuit board.
 10. A device simulating a photoconductive surface for sensing the current distribution thereon in an electrophotographic printing machine of the type having corona generating means spraying ions to create a charge on the photoconductive surface, including: means, closely spaced to the corona generating means, for accumulating the ions formed by the corona generating means to produce a current flow, said accumulating means comprising a plurality of substantially equally spaced electrically conductive portions insulated from one another; and means, in electrical communication with said accumulating means, for sensing the current flow on each portion of said accumulating means to detect the spatial distribution of the current flow produced by the corona generating means.
 11. A device as recited in claim 9, wherein said current sensing means includes: switch means in electrical communication with said accumulating means; and current measuring means in electrical communication with said switch means, said switch means being adapted to electrically connect each portion of said accumulating means to said current measuring means to detect the current flow thereon.
 12. A device as recited in claim 11, further including a pair of resistance elements, one of said resistance elements being electrically connected in series between said current measuring means and the portion of said accumulating means in electrical communication therewith, the other of said resistance elements being electrically connected in series between the other portions of said accumulating means and an electrical ground.
 13. A device as recited in claim 11, wherein the corona generating means of the electrophotographic printing machine includes: an elongated shield defining an open ended chamber; and a corona discharge electrode disposed in the open ended chamber of said shield.
 14. A device as recited in claim 13, wherein said discharge electrode includes at least a pair of spaced substantially parallel conductive coronode wires, said pair of coronode wires extending substantially in a longitudinal direction along the length of said shield.
 15. A device as recited in claim 14, further including grid means comprising a plurality of spaced substantially parallel grid wires mounted in said shield and extending substantially in a longitudinal direction along the length thereof, said plurality of grid wires partially enclosing the open end of said shield with one of the coronode wires being disposed in the chamber therebeneath, the other of said coronode wires being disposed in the unenclosed portion of the chamber of said shield.
 16. A device as recited in claim 15, wherein said accumulating means includes an elongated surface having the electrically conductive portions thereof arranged along discrete regions of the longitudinal axis thereof, said elongated surface being closely spaced to said pair of coronode wires with the longitudinal axis of said elongated surface closely spaced from and substantially parallel to the longitudinal axes of said pair of coronode wires, said elongated surface being arrangEd such that each electrically conductive portion detects the current flow from the discrete region opposed therefrom along the longitudinal axes of said coronode wires.
 17. A device as recited in claim 16, wherein said accumulating means includes: a conductive arcuate member; and an insulating sheet mounted on the exterior peripheral surface of said arcuate member, said elongated surface being mounted on said insulating sheet such that each electrically conductive portion extends from one marginal region of said arcuate member to the other marginal region thereof with each electrically conductive portion being located on a discrete region of said arcuate member in the longitudinal direction thereof.
 18. A device as recited in claim 16, wherein said elongated surface includes a printed circuit board. 